The objective of this project is to acquire numerical data on the responses of cultured human and mammalian cells to densely ionizing radiations in order to apply these data to early testing of these radiations in clinical radiotherapy. Colony forming ability and cell life cycle analysis will be used to investigate practical and fundamental aspects of the radiation responses of human cells to alpha particles, pions, neutrons, heavy ions, and gamma rays. The effects of dose, LET, oxygen, cell synchrony, ploidy, and nuclear size on cell survival and multiplication rate will be interpreted in terms of cell inactivation theory and radiotherapeutic time-dose relationships. BIBLIOGRAPHIC REFERENCE: P. Todd. Biological Aspects of High LET Radiation Therapy. Radiology (1977), in press.